



<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  
  <title>Implementing Java-style getters and setters &mdash; Python Anti-Patterns  documentation</title>
  

  
  

  

  
  
    

  

  
  
    <link rel="stylesheet" href="../_static/css/theme.css" type="text/css" />
  

  
    <link rel="stylesheet" href="../_static/css/ribbon.css" type="text/css" />
  
    <link rel="stylesheet" href="../_static/css/font-awesome-4.1.0/css/font-awesome.min.css" type="text/css" />
  
    <link rel="stylesheet" href="../_static/css/menu.css" type="text/css" />
  
        <link rel="index" title="Index"
              href="../genindex.html"/>
        <link rel="search" title="Search" href="../search.html"/>
    <link rel="top" title="Python Anti-Patterns  documentation" href="../index.html"/>
        <link rel="up" title="Correctness" href="index.html"/>
        <link rel="next" title="Indentation contains mixed spaces and tabs" href="indentation_contains_mixed_spaces_and_tabs.html"/>
        <link rel="prev" title="__future__ import is not the first non-docstring statement" href="future_import_is_not_the_first_statement.html"/> 

</head>

<body class="wy-body-for-nav" role="document">

  <div class="wy-grid-for-nav">

    
    <nav data-toggle="wy-nav-shift" class="wy-nav-side">
      <div class="wy-side-nav-search">
        <a href="../index.html"> Python Anti-Patterns</a>
        <div role="search">
  <form id ="rtd-search-form" class="wy-form" action="../search.html" method="get">
    <input type="text" name="q" placeholder="Search docs" />
    <input type="hidden" name="check_keywords" value="yes" />
    <input type="hidden" name="area" value="default" />
  </form>
</div>
      </div>


      <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation">
        
        
            <ul class="current">
<li class="toctree-l1 current"><a class="reference internal" href="index.html"><i class="fa fa-check"></i> Correctness</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="accessing_a_protected_member_from_outside_the_class.html">Accessing a protected member from outside the class</a></li>
<li class="toctree-l2"><a class="reference internal" href="assigning_a_lambda_to_a_variable.html">Assigning a <cite>lambda</cite> expression to a variable</a></li>
<li class="toctree-l2"><a class="reference internal" href="assigning_to_builtin.html">Assigning to built-in function</a></li>
<li class="toctree-l2"><a class="reference internal" href="bad_except_clauses_order.html">Bad except clauses order</a></li>
<li class="toctree-l2"><a class="reference internal" href="bad_first_argument_given_to_super.html">Bad first argument given to <code class="docutils literal notranslate"><span class="pre">super()</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="else_clause_on_loop_without_a_break_statement.html"><code class="docutils literal notranslate"><span class="pre">else</span></code> clause on loop without a <code class="docutils literal notranslate"><span class="pre">break</span></code> statement</a></li>
<li class="toctree-l2"><a class="reference internal" href="exit_must_accept_three_arguments.html"><code class="docutils literal notranslate"><span class="pre">__exit__</span></code> must accept 3 arguments: type, value, traceback</a></li>
<li class="toctree-l2"><a class="reference internal" href="explicit_return_in_init.html">Explicit return in __init__</a></li>
<li class="toctree-l2"><a class="reference internal" href="future_import_is_not_the_first_statement.html"><code class="docutils literal notranslate"><span class="pre">__future__</span></code> import is not the first non-docstring statement</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">Implementing Java-style getters and setters</a></li>
<li class="toctree-l2"><a class="reference internal" href="indentation_contains_mixed_spaces_and_tabs.html">Indentation contains mixed spaces and tabs</a></li>
<li class="toctree-l2"><a class="reference internal" href="indentation_contains_tabs.html">Indentation contains tabs</a></li>
<li class="toctree-l2"><a class="reference internal" href="method_could_be_a_function.html">Method could be a function</a></li>
<li class="toctree-l2"><a class="reference internal" href="method_has_no_argument.html">Method has no argument</a></li>
<li class="toctree-l2"><a class="reference internal" href="missing_argument_to_super.html">Missing argument to <code class="docutils literal notranslate"><span class="pre">super()</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="mutable_default_value_as_argument.html">Using a mutable default value as an argument</a></li>
<li class="toctree-l2"><a class="reference internal" href="no_exception_type_specified.html">No exception type(s) specified</a></li>
<li class="toctree-l2"><a class="reference internal" href="not_using_defaultdict.html">Not using <code class="docutils literal notranslate"><span class="pre">defaultdict()</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="not_using_else_in_a_loop.html">Not using <code class="docutils literal notranslate"><span class="pre">else</span></code> where appropriate in a loop</a></li>
<li class="toctree-l2"><a class="reference internal" href="not_using_explicit_unpacking.html">Not using explicit unpacking</a></li>
<li class="toctree-l2"><a class="reference internal" href="not_using_get_to_return_a_default_value_from_a_dictionary.html">Not using <code class="docutils literal notranslate"><span class="pre">get()</span></code> to return a default value from a dict</a></li>
<li class="toctree-l2"><a class="reference internal" href="not_using_setdefault_to_initialize_a_dictionary.html">Not using <code class="docutils literal notranslate"><span class="pre">setdefault()</span></code> to initialize a dictionary</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../maintainability/index.html"><i class="fa fa-puzzle-piece"></i> Maintainability</a></li>
<li class="toctree-l1"><a class="reference internal" href="../readability/index.html"><i class="fa fa-eye"></i> Readability</a></li>
<li class="toctree-l1"><a class="reference internal" href="../security/index.html"><i class="fa fa-lock"></i> Security</a></li>
<li class="toctree-l1"><a class="reference internal" href="../performance/index.html"><i class="fa fa-dashboard"></i> Performance</a></li>
<li class="toctree-l1"><a class="reference internal" href="../django/index.html"><i class="fa fa-book"></i> Django</a></li>
</ul>

        
      </div>
      &nbsp;

    </nav>

    <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">

      
      <nav class="wy-nav-top" role="navigation" aria-label="top navigation">
        <i data-toggle="wy-nav-top" class="fa fa-bars"></i>
        <a href="../index.html">Python Anti-Patterns</a>
      </nav>


      
      <div class="wy-nav-content" id="signup-box" >
        <div class="rst-content">
          <div class="navigation" role="navigation" aria-label="breadcrumbs navigation">
  <ul class="wy-breadcrumbs">
    <li><a href="../index.html">Documentation</a> &raquo;</li>
      
          <li><a href="index.html"><i class="fa fa-check"></i> Correctness</a> &raquo;</li>
      
    <li>Implementing Java-style getters and setters</li>
      <li class="wy-breadcrumbs-aside">
        
          <a href="../_sources/correctness/implementing_java-style_getters_and_setters.rst.txt" rel="nofollow"> View page source</a>
        
      </li>
  </ul>
  <hr/>
</div>

          <div role="main">
            
  <div class="section" id="implementing-java-style-getters-and-setters">
<h1>Implementing Java-style getters and setters<a class="headerlink" href="#implementing-java-style-getters-and-setters" title="Permalink to this headline">¶</a></h1>
<p>Python is not Java. If you need to set or get the members of a class or object, just expose the member publicly and access it directly. If you need to perform some computations before getting or setting the member, then use Python’s built-in <code class="docutils literal notranslate"><span class="pre">property</span></code> decorator.</p>
<div class="section" id="anti-pattern">
<h2>Anti-pattern<a class="headerlink" href="#anti-pattern" title="Permalink to this headline">¶</a></h2>
<p>The programmer below comes to Python from a long career as a Java programmer. For every class member that he wants to expose publicly, he defines a <code class="docutils literal notranslate"><span class="pre">get</span></code> and <code class="docutils literal notranslate"><span class="pre">set</span></code> method for that member. This is common practice in Java, but is frowned upon in Python as a waste of time and a cause of unnecessary code.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Square</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">length</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_length</span> <span class="o">=</span> <span class="n">length</span>
    <span class="c1"># Java-style</span>
    <span class="k">def</span> <span class="nf">get_length</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_length</span>
    <span class="c1"># Java-style</span>
    <span class="k">def</span> <span class="nf">set_length</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">length</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_length</span> <span class="o">=</span> <span class="n">length</span>

<span class="n">r</span> <span class="o">=</span> <span class="n">Square</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="n">r</span><span class="o">.</span><span class="n">get_length</span><span class="p">()</span>
<span class="n">r</span><span class="o">.</span><span class="n">set_length</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="best-practice">
<h2>Best practice<a class="headerlink" href="#best-practice" title="Permalink to this headline">¶</a></h2>
<div class="section" id="access-the-members-directly">
<h3>Access the members directly<a class="headerlink" href="#access-the-members-directly" title="Permalink to this headline">¶</a></h3>
<p>In Python it is acceptable to simply access class or object members directly. The modified code below exposes the <code class="docutils literal notranslate"><span class="pre">length</span></code> member as a public member. This is signified by the fact that there is no underscore character at the beginning of the member name. The <code class="docutils literal notranslate"><span class="pre">get_length()</span></code> and <code class="docutils literal notranslate"><span class="pre">set_length()</span></code> methods are no longer necessary so they have been deleted.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Square</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">length</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">length</span> <span class="o">=</span> <span class="n">length</span>

<span class="n">r</span> <span class="o">=</span> <span class="n">Square</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="n">r</span><span class="o">.</span><span class="n">length</span>
<span class="n">r</span><span class="o">.</span><span class="n">length</span> <span class="o">=</span> <span class="mi">6</span>
</pre></div>
</div>
</div>
<div class="section" id="use-built-in-property-decorator">
<h3>Use built-in <code class="docutils literal notranslate"><span class="pre">property</span></code> decorator<a class="headerlink" href="#use-built-in-property-decorator" title="Permalink to this headline">¶</a></h3>
<p>When a member needs to be slightly protected and cannot be simply exposed as a public member, use Python’s <code class="docutils literal notranslate"><span class="pre">property</span></code> decorator to accomplish the functionality of getters and setters.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Square</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">length</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_length</span> <span class="o">=</span> <span class="n">length</span>

    <span class="nd">@property</span>
    <span class="k">def</span> <span class="nf">length</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_length</span>

    <span class="nd">@length</span><span class="o">.</span><span class="n">setter</span>
    <span class="k">def</span> <span class="nf">length</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_length</span> <span class="o">=</span> <span class="n">value</span>

    <span class="nd">@length</span><span class="o">.</span><span class="n">deleter</span>
    <span class="k">def</span> <span class="nf">length</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">del</span> <span class="bp">self</span><span class="o">.</span><span class="n">_length</span>

<span class="n">r</span> <span class="o">=</span> <span class="n">Square</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="n">r</span><span class="o">.</span><span class="n">length</span>  <span class="c1"># automatically calls getter</span>
<span class="n">r</span><span class="o">.</span><span class="n">length</span> <span class="o">=</span> <span class="mi">6</span>  <span class="c1"># automatically calls setter</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="references">
<h2>References<a class="headerlink" href="#references" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li><p><a class="reference external" href="https://docs.python.org/2/library/functions.html#property">Python Built-in Functions - property</a></p></li>
<li><p><a class="reference external" href="http://dirtsimple.org/2004/12/python-is-not-java.html">dirtSimple - Python Is Not Java</a></p></li>
<li><p><a class="reference external" href="http://stackoverflow.com/questions/2627002/whats-the-pythonic-way-to-use-getters-and-setters">Stack Overflow - What’s the Pythonic Way to use getters and setters?</a></p></li>
</ul>
</div>
</div>


          </div>
          <footer>
  
    <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
      
        <a href="indentation_contains_mixed_spaces_and_tabs.html" class="btn btn-neutral float-right" title="Indentation contains mixed spaces and tabs"/>Next <span class="fa fa-arrow-circle-right"></span></a>
      
      
        <a href="future_import_is_not_the_first_statement.html" class="btn btn-neutral" title="__future__ import is not the first non-docstring statement"><span class="fa fa-arrow-circle-left"></span> Previous</a>
      
    </div>
  

  <hr/>

  <div role="contentinfo">
    <p>
    </p>
  </div>

    <!--End mc_embed_signup-->
  <a href="https://github.com/snide/sphinx_rtd_theme">Sphinx theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a> - Last updated: Sep 29, 2020 
</footer>
        </div>
      </div>

    </section>


  </div>
  


  

    <script type="text/javascript">
        var DOCUMENTATION_OPTIONS = {
            URL_ROOT:'../',
            VERSION:'',
            COLLAPSE_INDEX:false,
            FILE_SUFFIX:'.html',
            HAS_SOURCE:  true
        };
    </script>
      <script type="text/javascript" src="../_static/jquery.js"></script>
      <script type="text/javascript" src="../_static/underscore.js"></script>
      <script type="text/javascript" src="../_static/doctools.js"></script>
      <script type="text/javascript" src="../_static/language_data.js"></script>

  

  
  
    <script type="text/javascript" src="../_static/js/theme.js"></script>
  

  
  
  <script type="text/javascript">
      jQuery(function () {
          SphinxRtdTheme.StickyNav.enable();
      });
  </script>
   

  <!-- Place this tag right after the last button or just before your close body tag. -->
  <script async defer id="github-bjs" src="https://buttons.github.io/buttons.js"></script>

</body>
</html>